WASHINGTON — In the summer of 1987, just before my “television debut,” a true friend instructed me in a congressional hearing, “Remember, the microphone is always on — even when it’s not!” It’s a lesson I never have forgotten.

Apparently, Barack Obama doesn’t have any friends to give him similar advice, or he doesn’t learn well. Either way, an open mic during this week’s nuclear security summit in Seoul, South Korea, has revealed our president’s extraordinary hubris and his penchant for dangerous diplomatic duplicity.

The video clip of an unscripted exchange March 26 between Obama and outgoing Russian President Dmitry Medvedev should be grounds for the American people to hire a new commander in chief in November. The two leaders, evidently unaware they were being recorded, were discussing new limits on U.S. ballistic missile defense.

Obama: “On all these issues — but particularly missile defense — this can be solved, but it’s important for him to give me space.”

Medvedev: “Yeah, I understand. I understand your message about space — space for you.” Obama: “This is my last election. After my election, I have more flexibility.” Medvedev: “I understand. I (will) transmit this information to Vladimir.”

Note to reader: The “him” in Obama’s opening soliloquy and the “Vladimir” in Medvedev’s final remark are the same person: Vladimir Putin — the former and future president of Russia. On May 7, Putin and Medvedev exchange places in Moscow’s revolving-door government.

This surreal moment of unintended transparency from the Obama administration immediately went viral around the world. In Warsaw, where pro-U.S. politicians are still bruised from endorsing U.S.-built missile defenses — only to have the O-Team “postpone” the project — the president’s conversation is seen as proof that “Obama will cave in to Russia.” One Polish paper’s headline read, “Were they trading Poland?”

In the immediate aftermath, officials in Romania and the Czech Republic — both of which are slated for ballistic missile defense sites — wouldn’t comment on the Obama gaffe. But more than one political commentator observed that this is what we should expect from the Obama “reset” with Russia.

Unfortunately, the Obama reset hasn’t worked at all — and Putin didn’t need any privately delivered message from his lackey Dmitry to tell him that. Putin has been playing Obama as Yo-Yo Ma plays the cello. And now, thanks to what happened in Seoul, everyone can hear the music. The indelibly corrupt regime in Moscow has spurned every effort at improving relations with the U.S. and repeatedly used its veto threat in the United Nations Security Council to pre-empt any onerous sanctions against its clients in Iran and Syria.

Despite repeated entreaties from the White House to endorse Obama’s naive hope for “a world without nuclear weapons,” Putin is proceeding to quietly modernize Russia’s own arsenal — while we do not. Notably, Putin has spurned an invitation to the May 20-21 NATO summit in Chicago, where ballistic missile defense is on the agenda.

The fallout from the fiasco in Seoul is undoubtedly good news to the ayatollahs in Tehran. Buoyed by the precipitous withdrawal of all U.S. forces from Iraq last November and talk of an early pullout from Afghanistan, Iranian advocates for pressing ahead with their nuclear weapons program just gained further evidence that the American president is a paper tiger with a big mouth but no teeth.

The day after he bared his political soul in Seoul, Obama tried to make light of the matter. As he walked into the summit meeting, he clowned for the world press by placing his hand over the microphone on the dais and said, “Is the mic on?” They all laughed.

But it really isn’t a laughing matter. Who can imagine Ronald Reagan saying or doing such things anywhere — much less at a summit of world leaders — on or off mic? Can any of us recall Reagan in 1984 talking about “my” election? He knew it wasn’t his; it was ours.

We shouldn’t want a clown for a president. We ought to have a commander in chief who knows that his primary job is to protect the American people from harm. We deserve a head of state who will bow before God Almighty and no one else. And we need a chief executive who will tell the truth to our allies, our adversaries and, most importantly, the American people. It would be good to remember all this, particularly these dangerous diplomatic deceits, in November.